Method for welding thermoplastic foils

ABSTRACT

In a method for simultaneously welding to one another the layers of several pairs of thermoplastic foils arranged in a stack, a primary heat energy source is positioned between two pairs of thermoplastic foils, and welding heat energy is supplied to the two pairs via the primary heat energy source. The press for performing this method has two pressing elements for applying pressure to the stack of n pairs of layers of thermoplastic foils. The two pressing elements are positioned at opposite ends of the stack and force the layers of the pairs of thermoplastic foils toward one another. A stacked arrangement of n−1 flat, bar-shaped heating elements is aligned with the two pressing elements. Between two adjacent heating elements a respective pair of thermoplastic foils is received such that the pairs of thermoplastic foils alternate with the heating elements. The stacked arrangement of the heating elements is arranged in a plane that is perpendicular to the planes of the thermoplastic foils.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for simultaneously welding pairs oflayers of thermoplastic foils stacked atop one another with the aid ofwelding bars etc., that are brought into welding contact externally atthe stacked foil layers to load the foil layers against one another andto supply the welding heat.

2. Description of the Related Art

In a known method of this kind (German patent document 39 29 374), whichis designed for producing envelope-like or pocket-like articles, twopairs of layers of thermoplastic foil are pressed together by weldingbars with interposition of a stationary separating strip and are weldedtogether in that the welding energy for welding is provided in the formof heat supplied respectively by the welding bar that is facing theneighboring foil layer pair to that foil layer pair so that it is heatedto the welding temperature. The welding energy must flow through theproximal one of the two layers of the foil layer pair in order to alsoreach the area of the remote layer and to elevate its temperature to therequired melting temperature for the welding process. The requiredmelting energy thus must be transmitted via the outer (proximal) foillayer into the second (remote) one and bring the second one to thedesired melting temperature so that the fusing or connecting mechanismis in the end performed by a kneading action in the thermoplastic range.

In this manner, two foil layer pairs can thus be simultaneously welded.The welding process, however, is relatively time-consuming because thewelding energy requires a relatively long period of time in order toreach the interior of the contact area of the two foils of each foillayer pair. In particular when thicker foils are to be welded, thecorrespondingly required amount of time has been proven to be verydisadvantageous.

Of course, the afore mentioned method cannot be employed when more thantwo foil layer pairs are to be welded simultaneously to one another.

SUMMARY OF THE INVENTION

It is an object of the present invention to further develop the methodof the aforementioned kind such that with reduced amount of time thesimultaneous welding of two foil pairs is possible even when relativelythick foils are to be welded.

In accordance with the present invention, this is achieved in that, whentwo foil layer pairs are to be welded, the welding heat is supplied tothese two foil layer pairs preferably from the interior by employing aheat energy source which is arranged between the two foil layer pairsand, optionally, additional (ancillary) welding heat is provided bymeans of an ancillary energy source.

The method according to the invention, with which the aforementionedobject is solved, is characterized in that, when two foil layer pairsare used, these two foil layer pairs are supplied with the welding heator welding energy from the interior by employing a heat energy sourcepositioned between the two foil layer pairs and, optionally, in thatadditional welding energy is supplied from the exterior by an ancillaryenergy source.

In this way, the area where the welding seam is to be formed on the foillayer pairs can be heated in a very simple manner and within a shortperiod of time to the required welding temperature. As an ancillaryenergy source the use of welding bars or the like, which force the foillayer pairs against one another by loading them externally, has beenfound to be beneficial. When employing the inventive method, the use ofa bar-shaped, inwardly positioned, flat energy source as the interposedprimary heat energy source has been proven to be especially expedient.

A further very advantageous embodiment of the method according to theinvention employs n−1 bar-shaped, inwardly positioned (interposed) heatenergy sources for the simultaneous welding of n foil layer pairs. Thebar-shaped, inwardly positioned, heat energy sources release theirenergy in both directions, i.e., in the upward and downward directionsto the respectively adjacently positioned foil layer pairs. In this way,it is thus possible to subject several foil layer pairs, arranged in astack, to a simultaneous welding process in order to multiply in thismanner the number of envelope-like or pocket-like articles that can besimultaneously produced from thermoplastic foils.

In a variant of the inventive method, in addition to heating by means ofthe centrally arranged bar-shaped heating energy source positionedrespectively between two neighboring foil layer pairs, it is alsopossible to provide an external pressure loading by heated pressingplates.

The invention is not limited to a method but is also concerned with apress for performing the method. In accordance with the presentinvention, the press is characterized by two pressing elements forloading several, preferably n, foil layer pairs, wherein the pressingelements, preferably in the form of welding bars that are heatable, restagainst the outer ends of the stack of foil layer pairs and force thefoil layer pairs toward one another, as well as n−1 bar-shaped, flatenergy sources which are arranged in a plane which is positioned at aright angle to the foil planes.

This press according to an especially preferred embodiment ischaracterized by a removal device for a common removal of all of thefoil layer pairs, preferably by intermittent removal action, from thewelding area.

For augmentation of the removal of the foil layer pairs from the area ofthe bar-shaped, flat energy sources, it is advantageous when in the sameplane in which the bar-shaped flat energy sources are positioned, flatsupport elements are provided which have an outer coating thatsuppresses adhesion of the foil layer pairs.

The outer coating of the support elements is expediently aheat-resistant, resilient, especially wear-resistant, foil envelope madeof an insulating material, preferably PTFE (polytetrafluoroethylene),optionally containing embedded fiberglass. The foil envelope isexpediently provided at its side facing away from the foil layer pairswith an adhesive coating for fastening to the flat support elements.

It was found to be beneficial when the foil envelope is folded in aU-shape and guided about the bar-shaped, flat energy source so that thetwo legs of the U-shaped foil envelope rest on the oppositely positionedsurfaces of the flat support elements to form its outer coating.

For generating the heat energy, the bar-shaped flat energy sources canhave a flat, bar-shaped core as a support of an electrically heatableheating strip. In an especially expedient configuration, at least thatportion of the folded U-shaped foil envelope that contacts thebar-shaped core is formed by the electrically heatable heating strip.

The bar-shaped, flat energy sources can be most expediently realized byelectrically heatable nickel constantan bodies. The flat supportelements can be formed by sheet metal members which guide the foil pairsseparately through the press, wherein the sheet metal members preferablyhave a thickness of 2 to 3 mm.

In order to ensure in a simple manner the positioning of the sheet metalmembers, their lateral edge portions, which project past thelongitudinal edges of the thermoplastic foils, are expediently providedwith fixation bores for receiving fastening bolts.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1 is a schematic side view illustrating the press for performingthe welding method according to the invention, with two foil layer pairspassing through the press;

FIG. 2 is a schematic plan view onto the press according to FIG. 1;

FIG. 3 is a schematic view of the press according to FIG. 1 configuredfor welding more than two foil layer pairs; and

FIG. 4 is a view of the press according to FIG. 1, however provided withheated pressing plates instead of the more narrow welding bars.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inventive method can be performed with the aid of pressesschematically illustrated in the drawing. The inventive method isdesigned for simultaneously welding pairs 1, 1′ of layers ofthermoplastic foils stacked on top one another. They are simultaneouslywelded with the aid of welding bars 2, 3 which are brought into weldingcontact externally at the stacked foil layers, load the foil layersagainst one another, and supply the welding heat to the foil layer pairs1, 1′.

In methods of the prior art a stationary separation strip is providedbetween two neighboring foil layer pairs. The welding energy must besupplied by the neighboring welding bar and must then essentially flowthrough both layers of the foil layer pair in order to reach the area ofthe remote layer. This is disadvantageous because of the inherent timedelay. According to the invention, a more economical welding of the twofoil layer pairs 1, 1′ can be achieved in that the welding heat energyis not only supplied from the exterior via the welding bars 2, 3 thatload the outer sides of the foil layer pairs but also from the interiorby employing a heat energy source 4 positioned between the two foillayer pairs 1, 1′. This is realized expediently by employing abar-shaped, inwardly positioned, flat energy source as an interposedheat energy source (primary heating element) 4. Accordingly, n−1bar-shaped, inwardly positioned, flat energy sources 4, 4′, 4″, . . .are employed for the purpose of simultaneously welding n foil layerpairs 1, 1′, 1″ . . . , as shown in FIG. 3.

FIG. 4 shows an alternative method in which, in addition to heating withthe aid of the centrally arranged primary heat energy source 4positioned between two adjacently arranged foil layer pairs 1, 1′, apressing action is realized by employing heated pressing plates 5, 6 atthe outer sides (ends) of the stack of foil layer pairs.

The press for performing the method according to the invention isschematically illustrated in the drawing. It has two pressing elements2, 3, 5, 6 for loading several, preferably n, foil layer pairs 1, 1′, .. . by resting against the outer sides of the stacked foil layer pairsand forcing the pairs toward one another, as well as n−1 bar-shaped,flat energy sources (heating elements) 4, 4′, 4″, . . . arranged instacked arrangement in a common plane that is positioned at a rightangle (perpendicular) to the planes of the thermoplastic foils.Preferably, the pressing elements are welding bars 2, 3 that areheatable, thus providing an ancillary heating energy source.

Each press has coordinated therewith a removal device, illustrated onlyby the schematic representation of arrow 7 in the drawing, for theremoval, preferably in the form of an intermittent removal action, inthe direction of arrow 7 common to all foil layer pairs 1, 1′, 1″, . . .away from the welding area (defined by the welding bars).

In the same plane in which the bar-shaped flat energy sources 4, 4′, 4″,. . . are arranged, flat support elements 8, 8′, 8″, . . . arepositioned in a stacked arrangement. They have an outer coating forsuppressing the adhesion of the foil layer pairs 1, 1′, 1″, . . . Theouter coating of the support elements 8, 8′, 8″, . . . is formed by aheat-resistant and resilient, especially wear-resistant, foil envelope9, 9′, 9″, . . . made of insulating material, preferably PTFE(polytetrafluoroethylene), optionally containing embedded fiberglass.

Each one of the foil envelopes 9, 9′, 9″, . . . is provided at its sidefacing away from the neighboring foil layer pairs 1, 1′, 1″, . . . withan adhesive coating for fastening the foil envelope 9, 9′, 9″, . . . tothe flat support elements 8, 8′, 8″, . . .

The drawing shows that each foil envelope 9, 9′, 9″, . . . is folded toform a U-shape and is guided about the bar-shaped, flat energy source 4,4′, 4″, . . . so that the two legs of the U-shape rest against theopposite surfaces of the flat support elements 8, 8′, 8″, . . . and formits outer coating.

According to one embodiment of the inventive press, the bar-shaped, flatenergy sources 4, 4′, 4″, . . . comprise a flat, bar-shaped core as asupport for an electrically heatable heating strip. This can be achievedin the simplest fashion in that at least the portion of the U-shapedfolded foil envelope 9, 9′, 9″, . . . which is in contact with thebar-shaped core ,of the energy source is embodied as an electricallyheatable heating strip.

According to one alternative it is also possible that the bar-shaped,flat energy source 4, 4′, 4″, . . . is formed by electrically heatablenickel constantan bodies. The plan view of FIG. 2 shows that the flatsupport elements 8, 8′, 8″, . . . are formed by sheet metal membershaving preferably a thickness of 2 to 3 mm and guiding the foil pairs 1,1′, 1″, . . . separately and intermittently through the press in thedirection of arrow 7. Moreover, FIG. 2 shows that the sheet metalmembers 8, 8′, 8″, . . . have lateral edge portions 10 which projectpast the longitudinal edges 11 of the foil layer pairs 1, 1′, 1″, . . .and are provided with fixation bores 12 for receiving fastening bolts(not represented).

In analogy to this configuration, the laterally projecting ends of theflat energy sources 4, 4′, 4″, . . . are provided with electrical supplybores 13.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the inventive principles, it will beunderstood that the invention may be embodied otherwise withoutdeparting from such principles.

What is claimed is:
 1. A press for simultaneously welding the layers forseveral pairs of thermoplastic foils, the press comprising: two pressingelements for applying pressure to a stack of n pairs of layers ofthermoplastic foils, wherein the two pressing elements are positioned atopposite ends of the stack and force the layers of the pairs ofthermoplastic foils toward one another; and a stacked arrangement of n−1heating elements aligned with the two pressing elements and configuredto receive between two adjacent ones of the heating elements one of thepairs of thermoplastic foils such that the pairs of thermoplastic foilsalternate with the heating elements, wherein the stacked arrangement ofthe heating elements is arranged in a plane that is perpendicular to theplanes of the thermoplastic foils.
 2. The press according to claim 1,wherein the pressing elements are heatable welding bars.
 3. The pressaccording to claim 1, further comprising a removal device configured toremove the n pairs from the area of the two pressing elements and thestacked arrangement in a common removal direction.
 4. The pressaccording to claim 1, further comprising n−1 support elements arrangedin a stack positioned upstream of the stacked arrangement of the heatingelements in a transport direction of the pairs of thermoplastic foilsthrough the press, wherein the flat support elements are respectivelyaligned with the heating elements in a common plane parallel to theplanes of the thermoplastic foils, and wherein the flat support elementshave a coating suppressing adhesion of the thermoplastic foils.
 5. Thepress according to claim 4, wherein the coating is comprised of aheat-resistant and wear-resistant foil envelope made of insulatingmaterial.
 6. The press according to claim 5, wherein the insulatingmaterial is polytetrafluoroethylene.
 7. The press according to claim 5,wherein the insulating material contains embedded fiberglass.
 8. Thepress according to claim 5, wherein the foil envelope has an adhesivecoating on a side thereof facing away from the pairs of thermoplasticfoils and wherein the foil envelope is fastened with the adhesivecoating to the flat support element.
 9. The press according to claim 5,wherein the foil envelope has a U-shape such that the foil envelope isplaced onto one surface of the flat support element, is guided about theadjacently positioned heating element, and then folded back onto theopposite surface of the flat support element.
 10. The press according toclaim 9, wherein each of the heating elements is comprised of a flat,bar-shaped core and an electrically heated heating strip mounted on theflat core.
 11. The press according to claim 10, wherein the heatingstrip is a part of the foil envelope.
 12. The press according to claim4, wherein the flat support elements are sheet metal members configuredto separately guide the pairs of thermoplastic foils.
 13. The pressaccording to claim 12, wherein the sheet metal members have a thicknessof 2 to 3 mm.
 14. The press according to claim 12, wherein the sheetmetal members have lateral portions projecting past longitudinal edgesof the thermoplastic foils in a direction perpendicular to a transportdirection of the thermoplastic foils, wherein the lateral portions havefixation bores configured to receive securing bolts.
 15. The pressaccording to claim 1, wherein the heating elements are electricallyheatable nickel constantan bodies.